In the existing Global System for Mobile Communications (referred to as GSM) system, both a Mobile Switching Center Server (referred to as MSC Server) and a Media Gateway (referred to as MGW) are integral parts of a Core Network (referred to as CN). A Base Station Subsystem (referred to as BSS) consists of a Base Station Controller (referred to as BSC) and a Base Transceiver Station (referred to as BTS). An interfaces through which the MSC Server and the MGW communicate with the BSC is called A interface, the BTS is connected with the BSC via an Abis interface, and the BTS communicates with a Mobile Station (referred to as MS) through an air interface of Um interface.
At present, in a calling and called process of the GSM system, a user-plane speech of a caller party is transferred to the Media Gateway via the BSS, and then is transferred to the BSS of an opposite party, even if the two parties of a call are in the same BSS. However, there are a large of number of Local Calls in an actual GSM network, that is, the two parties of the call belong to the same BSS, or belong to the different BTSs of the same BTS cluster, or belong to the same BSC. For the local calls, the following questions will appear if the current call handling process is followed.
For calls belonging to the same BTS, the following case that a user-plane speech of a caller party is transferred to the BSC via the Abis interface of the BTS, the BSC transfers the user-plane speech to the MGW via the A interface, the MGW transfers the user-plane speech to the original BSC via the A interface, and then the original BSC transfers the user-plane speech to the original BTS, will occur. The aforementioned transmission mode results in the waste of transmission resources between the Abis interface and the A interface.
For calls belonging to the different BTSs of the same BTS cluster, the following case that a user-plane speech of a caller party is transferred to the BTS controlled by the BTS cluster via the Abis interface of the BTS, the controlled BTS transfers the user-plane speech to the BSC via Abis interface of the BTS, the BSC transfers the user-plane speech to the MGW via the A interface, the MGW transfers the user-plane speech to the original BSC via the A interface, the original BSC transfers the user-plane speech to the above controlled BTS, and then the above controlled BTS transfers the user-plane speech to the original BTS, will occur. The aforementioned transmission mode results in the waste of transmission resources of the Abis interface between the above controlled BTS and the BSC, as well as the waste of transmission resources of the A interface.
For calls belonging to the same BSC, as shown in FIG. 1, the case that the BSC transfers a user-plane speech to the MGW via the A interface at first, and then the MGW transfers the user-plane speech to the BSC via the A interface, will occur, thus resulting in the waste of transmission resources of the A interface.
In order to avoid this type of the waste of the transmission resources, a local switch function is provided. The local switch function refers to a function of switching speech data of the two parties through BSS, and the switch of the user-plane speech of the two parties is performed by the BSC for the two parties of the call under the same BSS, just as shown in FIG. 2. However, if one party of the call needs to perform the handover after using the local switch, such as needing to perform the handover from the original BSS to another BSS, the two parties of the call are no longer provided with services by the same BSC, therefore the local switch function will no longer continue to be used.
When a call using the local switch function needs to be handed over, the method adopted by the existing scheme is to stop using the local switch at first, to restore the mode of switching through the core network, and then to hands over in accordance with the existing handover process, as shown in FIG. 3. However, the method requires releasing the local switch at first, and then executes the handover, thus deferring the time of handover. At the same time, the local switch is also required to be established again if the handover fails.